In an office, each staff member is provided with an electrical device such as a personal computer, for example. Electric power from a power supply apparatus is supplied to the electrical device even in standby of the electrical device, so that a larger amount of electric power is consumed in an office compared to an ordinary household.
For lowering power consumption, a method for measuring power consumption of an electrical device to get a staff member to acknowledge a measurement result is effective.
On the other hand, recently, in an office, a sitting room where a staff member does not have a designated seat, which is called a free address, is employed. A staff member is frequently able to move with an electrical device. In order to measure power consumption of an electrical device, it is important to grasp which of power plugs of electrical devices is inserted into which of electrical outlets of power supply apparatuses.
For example, Japanese Laid-Open Patent Publication No. 2006-245983 describes that a power plug of an electrical device is provided with a current sensor and an RFID tag, and a power supply apparatus is provided with a reader/writer. Additionally, a technique has been proposed therein for detecting which of power plugs is inserted into which of electrical outlets.
Incidentally, a power supply apparatus has a structure including a plurality of electrical outlets. The plurality of electrical outlets is close to one another to be inserted into the power supply apparatus. As described in Japanese Laid-Open Patent Publication No. 2006-245983, identification of a power plug with an RFID tag causes interference because of using the same close proximity frequency band. As the result, it becomes difficult to grasp a correspondence relation between the power plug and the electrical outlet, which poses a problem.